Floating roof for a liquid storage tank



F. D. MOYER ET AL 3,057,507

FLOATING ROOF FOR A LIQUID STORAGE TANK Oct. 9, 1962 2 Sheets-Sheet 1Filed Jan. 23, 1961 five 7%215: Wedera'cijjgyev;

Oct. 9, 1962 F. D. MOYER ET AL 3,057,507

FLOATING ROOF FOR A LIQUID STORAGE TANK Filed Jan. 23, 1961 2Sheets-Sheet 2 I I Eva/$30245,

United States Patent 3,057,507 FLOATING ROOF FOR A LIQUID STORAGE TANKFrederick I). Moyer, Chicago, and Clifiord M. Orr, Western Springs, IiL,assignors to Chicago Bridge 3; Iron Company, Chicago, Ill., acorporation of Illinois Filed Jan. 23, 1961, Ser. No. 84,287 Claims.(Cl. 22026) This invention relates to a floating roof and moreparticularly to a roof used in a liquid storage tank of thefield-erected type.

Floating roof storage tanks have been used particularly extensively inthe petroleum industry to store exceedingly large amounts of product.The tank is an upwardly open circular shell with a bottom. The floatingroof covers most of the liquid surface of the product, there being aslight annular opening between the roof and the shell which is sealedagainst escape of vapors by a curtain.

The floating roof structures must be made to withstand and holdconsiderable rain water, particularly in climates where rainfall isquite heavy in quantity during a short time. In order to withstand thestresses without collapsing, roofs have been made in the past quiteheavy with sufficient bracing so that the roof may safely carryconsiderable loads. It is desirable to decrease the Weight of the roofin order that less steel be used in its manufacture. Stability underheavy rainfall conditions must be maintained however.

The present roof structure incorporates a simple design which actsdifferently under conditions of normal use and under the conditions ofheavy rainfall upon the roof. The roof weighs considerably less thanprevious floating roofs for use in the same size tank. It is extremelystable both under conditions of trapped water on the roof or in theevent of a rupture of a part of the roof which allows product to flow ontop of the roof.

Preferred embodiments of the present invention are illustrated in theaccompanying drawings in which:

FIGURE 1 is a top plan view of a liquid storage tank having the roof ofthis invention mounted thereon (the roof is shown in a very small scalein order to show the whole structure);

FIGURE 2 is a vertical sectional view taken substantially through thecenter of the tank and roof shown in FIGURE 1;

FIGURE 3 is a fragmentary broken enlarged sectional view along a radialline through the roof showing the details thereof;

FIGURE 4 is a view similar to FIGURE 3 showing the roof under conditionsof heavy rainfall thereon;

FIGURE 5 is a view similar to "FIGURE 2 of a slightly modified form ofthe roof;

FIGURE 6 is an enlarged fragmentary sectional view on a radial linethrough the roof shown in FIGURE 5;

FIGURE 7 is a fragmentary enlarged plan view of one end of the draintrough connection to the pontoon; and

FIGURE 8 is a fragmentary enlarged vertical sectional view through thestructure illustrated in FIGURE 7.

The liquid storage tanks in which floating roofs are generally used inthe petroleum industry include a plate bottom 9 (FIGURE 2) mounted upona prepared grade of sand fill or similar foundation. The bottom may beconed slightly toward the center in order to drain any water which maysettle from the petroleum product. The shell 10 of the tank is made ofhorizontal courses of butt welded or lapped plates, one upon the otherto the desired height. Various appurtenances are used with the tankssuch as the necessary piping and valves, gauging apparatus, accessladders and other equipment. These are not shown as they form no part ofthe present invention.

In FIGURE 2, stored liquid 11 is shown within the tank so that thefloating roof, generally designated 12, floats on the liquid near thetop of the tank.

The floating roof structure of the present invention in general includesan annular pontoon 13, which is spaced when the roof is centrallylocated within the tank a short distance from the inner surface of thesidewall 10 of the tank. The space within the pontoon is covered by asingle deck portion formed of plates lapped and welded together andsuitably secured to the inner periphery of the annular pontoon 13. Acentral sump 15 is formed by placing a plate ring 16 (FIGURE 3) inupstanding relation to the deck 14- substantially at the center of thedeck. Radial drain troughs 1'7 connect the upper surface of the annularpontoon 13 with the sump 15 so that rainfall falling on the roof will becollected in the sump more rapidly than on the rest of the single deckportion of the roof. A drain basin 18 is connected with the sump andwith the single deck portion outside the sump. With some products, rainwater may be drained directly through the product to the bottom of thetank. With others, a flexible hose or swingable pipe drain may beconnected to the drain basin and led outside.

Referring particularly to FIGURES 3 and 4, it will be noted that theannular pontoon 13 has an outer rim 19 extending substantiallyvertically and spaced a short distance from the wall 10 of the tank.This rim supports a conventional sealing structure (not shown),including, for example, shoes for sliding engagement with the tanksidewall and a curtain to seal the space against vapor loss. The bottom24 of the pontoon is connected to the lower end of the rim l9 and thetop and upper deck 21 is also connected to the rim so that it is pitchedtoward the center of the roof. An inner rim plate 22 joins the upper andlower decks of the pontoon and extends by a portion 23 above the upperdeck 21. This annular extension 23 serves to keep rain water that fallson the pontoon from passing inwardly of the upper deck and onto thesingle deck portion 14 of the roof.

As previously stated, the single deck portion 14 is of single platethickness. The sump is formed by the ring 16 suitably attached as byWelding to the surface of the single deck. As an example, the ring 16may be of a size to enclose an area equal to about one-fifth of theannular pontoon area. The drain troughs 17 thus will serve to collectwater within the sump six times as rapidly as water will be collectedupon the single deck portion 14. The practical result of this operationis that the center of the deck is thus weighted by the collected waterdepressing the single deck deeper into the product so that the drainagepitch or slope of the single deck portion is increased.

Water collected on the single deck portion is conducted into the basin18 through an opening 24 adjacent the upstanding rim 16. A smalleropening 25 may also be provided into the basin and communicating withthe sump. However, an upstanding pipe 26 of much larger size than theopening 25 will serve to maintain most of the water in the sump untilafter the water has been drained from the single deck portion. The smallopening 25 may be omitted and the drain pipe 26 will thus maintain waterWithin the sump during periods of no rainfall and the water willgradually evaporate. An

. emergency overflow pipe 27 may be provided communitakes up in ringcompression the forces which the single deck imposes on the pontoon. Thedrainage troughs 17 are suitably connected to the pontoon inner rim 22by a thin flexible metal angle 29 (FIGURES 7 and 8). The inner end 30 ofthe troughs merely rests upon the upstanding rim 16 in slidingengagement so that it may move with up and down movements of the singledeck portion.

The pontoon 13 is designed to support the roof under the most severeconditions to which the roof may be subjected. This condition mightexist should the drain become clogged or should the single deck portionbe ruptured so as to permit product to flow onto the single deckportion.

The embodiment illustrated in FIGURES and 6 differs from that of FIGURES3 and 4 in that a step is provided in the single deck portion. Thesingle deck sump floor 31 is connected to the upstanding sump ring 16 atan elevation above the connection of the single deck portion 32 outsideof the ring to provide a step in the single deck portion at the sumpring. The ring is made larger since the depth of liquid that can becollected inside the sump is less than in the case of the roof shown inFIGURES 3 and 4. This structure provides an even increased pitch to thesingle deck portion 32 when rain water is collected in the sump todepress the single deck portion. Additional stiffening angles 33 arerequired at the connection of the sump floor 31 to the ring and thusincrease slightly the weight of the roof over that shown in FIGURES 3and 4. The weight, however, is still considerably less than required inother roof designs.

In operation, both of the forms of the roof described above have theadvantage of providing a Weight on the center of the roof to depress thesingle deck portion and increase the drainage characteristics during thetime that such drainage is required in normal operation. In dry periods,the rain water is removed from the roof so that the single deck portionmerely floats on the liquid without necessarily great slope or pitchtoward the drain. This structure permits a substantial reduction in theoverall weight of the roof without adverse effect on the performancethereof.

The foregoing detailed description has been given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom, for some modifications will be obvious to those skilled inthe art.

We claim:

1. A floating roof for a liquid storage tank, comprising: an annularhollow pontoon having an inwardly sloping upper deck and an inner rimplate extending above said deck to trap rain water thereon; a relativelyflexible single plate thickness deck secured to the pontoon below theinner edge of the sloping upper deck and covering the area Within thepontoon; an upstanding plate member secured to the single deck forming asump generally centrally of the single deck; and a drain troughextending over the single deck from the pontoon upper deck to the sumpto drain and collect rain water into the sump during rainfall morerapidly than on the single deck outside the sump.

2. A floating roof as specified in claim 1 wherein a drain is connectedto the single deck outside the sump and an overflow drain is positionedin the sump with its inlet spaced above the bottom thereof so that rainwater may collect in the sump to depress the central portion of thesingle deck to improve drain slope of the deck during rainfall.

3. A floating roof as specified in claim 1 wherein the plate memberforming the sump is a ring secured to the single deck plate and extendsupwardly from the deck forming said sump.

4. A floating roof as specified in claim 1 wherein the single deckportion outside the plate member forming said sump is secured to thelower end of the plate member and the single deck portion inside theplate member is secured thereto above the lower end to form a step inthe single deck for sloping the outer single deck portion toward thesump.

5. A floating roof as specified in claim 1 wherein said drain trough isflexibly secured to the pontoon at its outer end and slidingly rests onthe plate member at its inner end and extends in bridge fashion over theintervening single deck.

References Cited in the file of this patent UNITED STATES PATENTS2,390,141 Wiggins Dec. 4, 1945 2,497,047 Prager et a1. Feb. 7, 19502,538,033 Orr Jan. 16, 1951 2,886,204 Moyer et a1 May 12, 1959

